The present Invention relates to a projection type liquid crystal display device using liquid crystal display elements, and in particular to a projection type liquid crystal display device having a small size and a good image quality performance such as brightness, etc.
Heretofore, as an image display device, there is known a projection type display device, in which an optical image formed on light valves as variations in optical characteristics, depending on image signals, is illuminated by means of illumination optics to be enlarged and projected on a screen by means of projection optics. A number of projection type liquid crystal display devices have been proposed, each of which uses liquid crystal display elements as light valves for such a display device. A twisted nematic (TN) type liquid crystal display element, which is a representative example of a liquid crystal display element, is so constructed that two polarizers are disposed before and after a liquid crystal cell, in which liquid crystal is injected between a pair of transparent base plates, each of which has a transparent electrode film, so that polarization directions thereof differ by 90xc2x0 from each other and a number of such liquid crystal display elements are arranged so that light intensity of incident light transmitted by each of them is controlled by combining an action to rotate a polarization plane by an electro-optical effect of the liquid crystal with an action to select a polarization component by one of the polarizers to display image information. Recently performance such as resolution, etc. is rapidly improved as down-sizing of such transmission type or reflection type liquid crystal display elements themselves is advanced so that down-sizing and improvement in performance of a display device using such liquid crystal display elements are advanced. In this way, projection type liquid crystal display devices have been newly proposed not only for conventional image display using video signals, etc. but also for image output devices of personal computers.
However a prior art projection type liquid crystal display device had problems that it has a large size and that performance such as brightness of image, etc. finally obtained is insufficient. Although downsizing of light valves, i.e. liquid crystal display elements themselves, is efficient for down-sizing of a whole display device, since an area illuminated by illumination optics is decreased, when the size of liquid crystal display elements is decreased, problems take place that a ratio of a light flux projected on liquid crystal display elements to a whole light flux emitted by a light source (hereinbelow called light utilization efficiency) is lowered, etc. As the result, it was difficult to realize down-sizing of the whole device and improvement of performance such as brightness, etc. at the same time. Further, in case of a projection type liquid crystal display device, since various factors such as optical characteristics of a projection lens, optical characteristics of liquid crystal display elements, etc. apart from the illumination optics have influences on image quality performance, it was difficult to obtain a display device having a small size and a good image quality performance, if only the illumination optics were improved.
A main object of the present invention is to provide a projection type liquid crystal display device having a small size and a good image quality performance.
Another object of the present invention is to raise utilization efficiency of light emitted from a light source.
Still another object of the present invention is to make brightness uniform over a whole screen.
According to the present invention, a projection type liquid crystal display device, which includes a light source; illumination optics having an action to irradiate a surface to be irradiated with light emitted by the light source; liquid crystal display elements modulating light; and projection optics for projecting light emitted by the liquid crystal display elements, is so constructed that the illumination optics have at least one elliptic mirror and one spherical mirror and that the illumination optics comprise further a first lens array and a second lens array, in which a plurality of lenses are arranged perpendicularly to an optical axis from the light source side, and a condenser lens for irradiating the liquid crystal display elements with light, which has been emitted by the second lens array, with a high efficiency.
In this way, it is possible to realize a bright projection type liquid crystal display device having a small size and a good image quality performance by raising utilization efficiency of light emitted by the light source.